High-frequency apparatus



Ott. 25, 1949. T. BOERNER ETAL.

HIGH-FREQUENCY APPARATUS Original Filed June 17, 1943 ha dalla,

n m d g3 OQ WQ @mi RFQ Patented Oct. 25, 1949 2,485,856 HIGH-FREQUENCY APPARATUS Thomas James Boerner, Collingswood,

and John W. Sanborn, Merchantville, N. J., assignors to Radio Corporation of America, a corporation of Delaware Original application Jun 491,164. Divided 28, 1944, Serial No.

6 Claims.

This is a. division of our copending application Serial No. 491,164, filed June 17, 1943, now Patent No. 2,412,314 issued December 10, 1946, and describes an invention which relates to high frequency apparatus and especially to the power amplifier stages of high frequency transmitters.

One object of the invention is to provide improved high frequency vacuum tube power amplifying apparatus and circuits which shall operate at high eiiiciency and in which spurious effects such as parasitic oscillations are minimized. A further object of our invention is to provide high frequency amplifying apparatus wherein the frequency of operation may readily and conveniently be changed.

In brief, certain features of the present invention may be outlined as follows:

A push-pull connected vacuum tube driver stage is coupled through a condenser-divider arrangement to a push-pull connected vacuum tube power amplifier. The condenser-divider operates in such a way that over a wide range of operating frequencies substantially constant radio frequency excitation is applied tothe grids of the power amplifier with constant direct current voltage impressed upon the plates of the driver tubes. In this connection it may also be mentioned that biasing circuits are provided for the grids of the power amplifier tubes which operate so as to secure flow of equal grid currents over a wide operating range.

Reversible electric motors are provided for adjusting neutralizing and tuning condensers of the power amplifier stage and output circuit, Further instrumentalities under control of other reversible electric motors are provided for adjusting other circuits, etc., as will be explained more fullylater. Limit switches are provided for the motors so as to prevent them from over-running in either direction. Instrumentalities are also provided whereby each reversible electric motor drives the variable arm of a potentiometer. Each potentiometer supplies voltage to a separate tuning indicator which may be in the form of a volt meter. AIn this way the tuning indicators give a measure, by the respective volt meter `readings, of the capacity in circuit and in other cases the amount of coupling or the amount of inductance in the power amplifier tank circuit.

I'he drawing is a wiring diagram of a pushpull connected driver-amplifier stage feeding through a condenser-divider arrangement the grids of a pair of push-pull connected vacuum tube amplifiers of a high frequency power amplifler. As illustrated, reversible electric motors e 17, 1943, Serial No.

and this application March are provided for varying neutralizing and tuning condensers, the inductance of the tank circuit, and the coupling between the tank circuit of the power amplifier and the final output circuit to which the tank circuit is coupled.

Referring to the drawing, any carrier frequency within a .range of, say, for example, 6 to 22 megacycles is fed into the primary coil |L|| and thence into the secondary |L|3, exciting the control grids of tubes IVI and |V8 in phase opposition. The carrier may be generated by any tube generator followed by ampliers and frequency multipliers. The secondary |L|3 is tuned by the split stator condenser |C4. The amplified output of the driver stage consisting of tubes lVl and |V8 appears in the tuned output circuit comprising coil |L|6 and condensers |C|0|, |C86, |C8`| and |C|04. The condensers are switched into the circuit as needed, depending upon the frequency employed.

In order to prevent spurious oscillations, the screen grids of the driver tubes |V1 and |V8 are by-passed to ground by condensers |046 and lC4'l. For a range of lower frequencies, additional by-passing condensers |C84 'and IC85 are also switched into the circuit, but are switched out of circuit in the range of higher frequencies. That is to say, condensers |C4'I and |C46 will serve to give sufficient by-passing to ground at the higher frequencies since these condensers may be constructed integrally with the screen grid connections to the tubes.

Over the entire range of frequencies, however, neutralizing condensers |068 and |069, which may consist of sections of copper strap adjacent the anodes, are also employed. That is, these neutralizing condensers are employed in addition to the screen grids and their by-passing circuits to ground, over the entire operating range of frequencies. The use of such neutralizing circuits in addition to the screening circuits insures freedom from spurious oscillations and similar effects.

Coupling from the driver stage, including tubes IVT and |V8, to the final power amplifier stage comprising water cooled tubes |V9 and |V|0, is accomplished through capacitors |C|0U, |048, |C|02, |C|03, |C49 and |C|05.

The condensers |C|00, |048 and |C|02 are equal in value, respectively, to condensers |C||)3, |C49 and ICIUS. The values of the upper three capacitors in parallel and the lower three are therefore equal; or, they may be used singlyor in pairs so that the coupling capacities on both sides of the plate coil |L|6 are equal. In this way, proper voltage will be applied to the grids of the final power amplifier tubes for different operating conditions.

From the foregoing, it will be observed that the input capacity of the power amplifier tubes IV9 and IVIU form the low voltage legs of a condenser divider. Hence, as long as the radio frequency plate voltage of the driver stage is held constant, the condenser divider serves to maintain a correspondingly constant excitation voltage to the power amplifier across the power tubes of IV9 and IVIO over a very wide frequency range.

By virtue of the condenser divider tuning of the driver output stage can be adjusted over the entire frequency range without affecting the ratio of driver plate to power amplifier grid radio frequency voltage. Actually some fixed adjustment of the coupling capacitors of the voltage divider arrangement may be required. We have found that the entire range from six to twentytwo megacycles can be covered with three com binations of the condensers in the voltage divider with wide non-critical points of overlap. Further adjustment n the circuits may be made by means of the taps on coil ILI 6 and by changing the position and coupling of a short-circuited turn ILISA with respect to the turns of coil ILIS.

The grids of the power amplifier tubes are subjected to biasing action through the action of a common resistor IRIUII and the further resistors IRIOIJA. As indicated, one of the latter is connected in series with the grid of tube IV9 and the other in series with the grid of the other tube IVIO of the power amplifier. Also, it will be noted that chokes IL50 and IL50A and radio frequency by-pass condenser ICI30 have been provided in the grid circuit of the power amplifier stage. The grid circuit as described provides balanced grid currents over the entire range of frequencies employed.

Neutralizing condensers ICI01 and ICIIIS, which will be described in greater detail hereinafter, are provided for the power amplifier tubes IV9 and IVIII. Also, as will be described more fully hereinafter, the tank circuit of the power amplifier comprises the inductance ILSI, tuning condenser ICI I2, short-circuiting strap SB, condenser ICI23, by-passing condenser ICI24 and choke IL5B.

The loading or output circuit, which also will be described more fully hereinafter, comprises the inductor IL52, tuning condenser ICIII and fixed-condensers ICI I5 to ICI |22 inclusive.

Motor-driven adjustment or tuning of various elements in the power amplifier stage and output circuit are provided. Thus, reversible electric motor IA2II drives neutralizing condensers ICIUG and ICI01. Direction of rotation is controlled by switch ISI. Limiting switches, diagrammatically indicated at ISI 2 and ISI3, limit the amount of rotation of the motor in either direction. 'I'he angular position of motor IA2II is indicated on a tuning indicator IMIS which is in effect avoltmeter, the voltage of which depends upon the position of tap 40B upony potentiometer IRIS. The tap 40B is moved along the potentiometer IRIS by the action of motor IA20. In other words, motor IA2II simultaneously varies condensers ICI06 and ICIII1 and the position of tap 40B along potentiometer IR,

Similarly, reversible driving motors IAN', IA2I, VIA24 and IA25, switches ISI, ISS, ISIB, and ISII, limiting switches ISIS, ISII, ISII, ISIS, ISIS, ISIS, IS2II and IS2I, and indicators IMIS,

IMII, IMIS and IMI1 are provided for adjusting and indicating the adjustment of condensers ICI I2, coupling between inductors IL5I and IL52 and condenser ICIIl. 4Supply voltage for the tuning indicating system is derived from the rectifier arrangement IA30. Motor driving power is furnished through leads IB and 2A. The power supply to these leads may be, for example, 220 volts 60 cycles A. C. current.

The limit switches, such as ISI2 and ISIS, may be operated by cams, in turn operated or driven by reduction gearing coupled to the motor IA2II, so thatafter a given number of revolutions in one direction, limit switch ISI2 will be opened and after a given number of revolutions in the other direction limit switch ISIS will be opened. Similarly, the potentiometer and tap arrangement IR|I3 and 40B may be controlled by reduction gearing also coupled to the motor IA2II, the tap being in contact with and moved over a circularly shaped potentiometer winding. Similar comments are applicable to the other limit switches and potentiometers controlling the tuning indicators TI. The latter are provided with by-passing condensers ICI5 to IClS inclusive.

Having thus described our invention, what we claim is:

l. A control system for high frequency apparatus having a push-pull connected vacuum tube power amplifier, comprising a variable condenser arrangement including at least two variable condensers, each one of said condensers connected to the respective vacuum tubes of said amplifier, a reversible electric motor, switching apparatus for controlling the direction of rotation of said motor in either direction, and mechanical linkage between the armature of said motor to a variable element on each one of said variable condensers, wherebyfmovement of said motor simultaneously varies each condenser cal pacity.

2. A control system for high frequency apparatus, comprising a. plurality of variable condenser and inductor impedance elements connected to said high frequency apparatus, a plurality of reversible electric motors there being a motor individual to each condenser and inductor element, switching apparatus for controlling the direction and the amount of rotation of each one of said motors, and mechanical linkage between said motors and the respective condensers and inductors, whereby the movement of said motors varies the reactance of the impedance element linked thereto.

3. A motor control system including a pushpull. connected vacuum tube amplifier, comprising a variable condenser arrangement including at least two variable condensers, each one of said condensers being connected to the respectivo vacuum tubes of said amplifier, a source of voltage, a reversible electric motor, a potentiometer, a meter, connections from said source of voltage to said potentiometer, a movable tap on said potentiometer, said meter being connected to one side of said potentiometer and its movable tap, switching apparatus for controlling the direction o! rotation of said motor and mechanical linkage between the armature of said motor and each one of said variable condensers and also said movable tap. whereby the movement of said motosI varies the values of said condensers and simultaneously the position of said tap, and the meter Indicates the angular position of said motor.

4. A control system for high frequency apparatus having a plurality of variable condensers and inductors connected to said high frequency apparatus, comprising a source of voltage, a plurality of electric motors, there being a motor controlling each condenser and a motor controlling each inductor, a plurality of meters, a plurality of potentiometers each having a movable tap, each one of said potentiometers being connected across said source of voltage, each one of said meters being connected to one side of each potentiometer and its movable tap, there being a potentiometer associated with each condenser and with each inductor, a link between the tap on each potentiometer and its associated motor, switching apparatus for controlling the direction and the amount of rotation of each one of said motors, whereby the movement of any motor varies the reactance of the condenser or induetor linked thereto and simultaneously causes the meter associated with its respective potentiometer to measure the change in said reactance.

5. A control system for high frequency apparatus having a plurality of variable condensers and an inductor connected to said high frequency apparatus comprising a source of voltage, a movable short-circuiting strap across a portion of said inductor, a plurality of electric motors, a plurality of meters, a potentiometer individual to each condenser and to said inductor, each potentiometer having a mcvable'tap, said potentiometers being connected across said source of voltage, each one of said meters being connected to one side of each potentiometer and its movable tap, switching apparatus for controlling the direction of the amount of rotation of each one of said motors, and mechanical coupling apparatus coupling said motors respectively to different condensers and to said short-circuiting strap, and linkage between each motor and the movable tap on its associated potentiometer, whereby the movement of one of said motors varies the capacity of a condenser and another motor moves said short-circuiting strap simultaneously, and the meters indicate the degree of movement of said motors.

6. A control system for high frequency apparatus including vacuum tube amplifiers connected in push-pull relationship comprising two vacuum tubes each having at least an anode, a grid and a cathode, two neutralizing condensers each in circuit connection between the anode of one tube and the grid of another tube, a source of voltage, a reversible electric motor linked to both neutralizing condensers for simultaneously varying the same, a potentiometer connected in shunt with said source of voltage, a variable tap for said potentiometer, said variable tap being linked to said motor, and a meter 1n shunt with said potentiometer.

THOMAS JAMES BOERNER. JOHN W. SANBQRN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,539,168 Dresser May 26, 1925 1,872,155 Masek Aug. 16, 1932 1,959,494 Nyquist May 22, 1934 2,096,072 Spagnola Oct. 19, 1937 2,098,587 Markowitz Nov. 9, 1937 2,147,486 Fyler Feb. 14, 1939 2,191,606 Butler Feb. 27, 1940 2,347,523 Suksdorf Apr. 25, 1944 2,376,667 Cunningham et al. May 22, 1945 

